A. Field of the Invention
The field of the present invention relates generally to sealed light fixtures, such as those utilized for outdoor lighting. More specifically, this invention relates to sealed light fixtures that utilize a valve to prevent condensation in the fixture and to vent pressure build-up therein. Even more specifically, the present invention relates to sealed light fixtures having valves that automatically vent pressure build-up in the sealed light fixture to create a vacuum therein that prevents condensation, yet facilitates assembly and disassembly of the light fixture by equalizing the pressure in the fixture with the atmosphere.
B. Background
It is well known that many people use lights, such as spotlights and other types of lights, in outdoor applications. These applications generally require a sealed or near-sealed light fixture to prevent moisture from entering the light housing, lamp or electrical circuit components of the lighting system to prevent damage or injury that can result from moisture contact with an electrical system. The typical outdoor light fixture has a mounting assembly that includes a knuckle joint that attaches to a junction box or other source of electricity, a housing connected to the knuckle joint and a cap connected to the housing to enclose the lamp. Gaskets are typically utilized between the various members of the light fixture to prevent the intrusion of moisture.
Despite the significant operational and safety advantages of using a completely sealed housing, the sealing of the housing makes assembly and disassembly of the light fixture very difficult. In order to assemble the light fixture, the cap must be placed on the housing and locked into place. If the housing is sealed such that the completed assembly will be airtight, the action of placing the cap on the housing compresses the air inside the housing and makes placement of the cap on the housing difficult. Once the cap is in place on the housing, the high internal pressures that exist make locking the cap to the housing very difficult. Brute force or some type of mechanical advantage must be used in order to seal the cap onto the housing. Once the cap is installed, the sealed light fixture must be able to withstand the increased internal pressure that results from the heating of the air inside the fixture when the lamp is on. The problems with utilizing a sealed housing are compounded with larger size light fixtures which generate more heat.
To avoid the problems described above, most light fixtures are manufactured so they are not completely air-tight. These systems have significant disadvantages. Fixtures that are not air-tight have a mechanism to vent the pressures that result from assembling the light fixture and the pressure that results from the heating up of air inside the housing during operation. Generally, the venting is accomplished by making the knuckle joint connector such that it is not air-tight where it connects to the housing. Because it is open to the atmosphere, the knuckle joint or other non-sealing mechanism allows air to vent out of the light fixture during installation and during the heat-up and expansion caused by the lamp being on.
Unfortunately, while the air inside the housing is cooling after the lamp is turned off, outside air is drawn inside the housing as the pressure inside the housing lowers. This drawing in of outside air brings moisture and contaminates that are also in the air (such as salt for installations near salt water) inside the housing. The resulting moisture inside the housing can cause condensation that can result in corrosion and/or problems with the electrical components. To avoid these problems, the internal components must be manufactured out of materials that can withstand corrosion and moisture must be prevented from entering into moisture-sensitive areas. Some manufacturers utilize chemical materials inside the light fixture to absorb the moisture that enters as a result of the above process.
As an alternative to the non-sealed light fixtures described above, some manufacturers of light fixtures create a vacuum inside the lamp housing during the manufacturing process. The vacuum inside the housing solves the problems with moisture and contaminates getting inside the housing and reduces or eliminates the problem with condensation. However, due to the vacuum, the owner of such a light fixture can only replace the lamp by removing the entire lamp housing and shipping it to the manufacturer for replacement. This creates significant difficulty and expense for the system owner.
What is needed is a sealed light fixture having a mechanism for releasing the pressure build-up that occurs during the installation of the cap onto the housing and which results from the temperature increase when the lamp is on, while preventing moisture and contaminates from entering the light fixture after the lamp turns off. The mechanism should also permit the light fixture owner to equalize the pressure inside the housing to allow relatively easy removal of the cap for relamping.